can的过去式英文

This could cause serious damage to the country's economy.

这可能对国家的经济造成严重破坏。

The database could be used as a teaching resource in colleges.

数据库可以用作大学里的一种教学辅助手段。

I think we could all use a drink after that!

我想我们在事情办完之后都得痛快地喝一杯。

He could just make out three people through the mist.

透过薄雾他勉强能看出有三个人。

The operation could prolong his life by two or three years.

这次手术可使他多活两三年。